The purpose of this work is to examine the chemical and biological properties of murine histocompatibility antigens (H-2) and tumor associated transplantation antigens (TATA) assayed by their ability to elicit tumor rejection in vivo. The approach is to purify the molecules expressing these antigens and determine their: 1) ability to induce in vivo immune responses such as tissue rejection and humoral response, 2) ability to stimulate in vitro immunity such as cytotoxic lymphocytes or lymphocyte proliferation, 3) ability to function as a function as a restriction element, 4) chemical properties with particular emphasis on how the molecules interact with the plasma membrane. Once these antigens are purified, monoclonal antibodies will be prepared to assist in the characterization of the molecules and their expression on tumor cells. Moreover, the availability of purified molecules and high titered antibodies will permit the preparation of suitable probes to study the organization and expression of the genes encoding these molecules. In the case of TATA it is hoped that this knowledge Results will contribute to a rational basis for in vivo therapeutic protocols.